(1) Field of the Invention
The invention relates to a diverter switch, in particular a single-channel diverter switch, for branching off bulk-material flows, having a rotary plug which is arranged in a stationary housing preferably comprising three connecting openings. More particularly the invention pertains to a novel labyrinth seal having one labyrinth seal groove with a rotary plug disposed around at least one opening of a through channel in which the labyrinth seal groove is arranged around at least one of the connecting openings.
(2) Description of the Related Art Including Information Disclosed Under 37 C.F.R. 1.97 and 1.98
Numerous different variants of diverter switches, in particular single-channel diverter switches or plug diverter switches, are already known. They generally have the task of feeding the bulk material to be conveyed to various pipelines by deflecting the conveying direction, a conveying gas in particular being used for conveying the bulk material.
In a corresponding diverter switch according to publication DE 39 22 240 C2, a cylindrical rotary plug is used, in which the inlet side and outlet side of the through-channel are transposed by the adjustment or rotation from a first position into a second position. In this case, flow occurs through the through-channel of the rotary plug in the second position against the direction of flow of the conveying fluid in the first position. The through-channel is arranged essentially perpendicularly to the rotation axis of the cylindrical rotary plug and often has a virtually round free cross section.
In corresponding single-channel diverter switches, depending on the length of the conveying path downstream of the deflection or downstream of the valve, considerable pressure differences can partly occur between the two outflow channels. Corresponding diverter switches normally have elastic seals in order to minimize leakages which occur. In this case, the leakages depend, inter alia, on the pressure of the conveying fluid or transport gas in comparison with the atmospheric ambient pressure and also on the above-mentioned pressure differences between the outflow channels.
Corresponding seals may be accommodated in the diverter switch housing or in the rotary plug. For example, these seals are designed as inflatable seals or as static seals, in particular provided with a special profile shape, which press automatically against the mating body when pressure builds up in the conveying line.
The publication DE 199 52 435 A1 discloses a switch for bulk material with an inlet channel and at least two outlet channels, it being possible with the aid of a rotary plug for the inlet channel to be optionally connected to one of the outlet channels. For sealing, the rotary plug has an elastomer seal.
In addition, diverter switches with a flap are also known (cf. DE 96 80 47). As a difference from rotary plugs, flaps have two mutually separate through-regions, to connect the inlet optionally to the two outlet channels. Consequently, a comparatively thin directing element which can swing back and forth between two positions is necessarily provided between the two through-regions. By contrast, a rotary plug of the generic type for diverter switches has only one through-channel, which, for connecting the inlet channel to the two outlet channels to be selected, must be adjusted in such a way that the direction of through-flow in the individual through-channel is reversed for the two positions.
A disadvantage with corresponding sealing systems, however, is that seal wear may occur, the corresponding seals being partly abraded. Since the seal material normally cannot be made of the same material as the bulk material to be conveyed, the abrasion of the seal leads to contamination of the material to be conveyed. In the case of very high-grade materials to be conveyed, or materials to be conveyed which are of very high purity, this abrasion is disadvantageous or even inadmissible. Used for such special applications are diverter switches which have as narrow a gap as possible between the plug and the housing in order thus to reduce the leakage losses.
In terms of construction, very high demands are made on the accuracy and guidance of the components, so that the established gap is retained in all operating states and material contact and possibly seizing or abrasion does not occur. The realization of comparatively narrow gaps between the plug and the housing therefore requires the plug and also the housing to be produced in a very complicated manner to close tolerances, which leads to economically unfavourable production of corresponding diverter switches.
In addition, the gaps which can currently be realized lead to unacceptable leakage losses in particular in plug diverter switches working under relatively high pressure differences. This may lead, for example, to malfunctions in the conveying operation, which has to be compensated for at considerable cost, if need be by additional, metered feeding of conveying gas directly downstream of the diverter switch. Sealing closure members connected downstream will possibly be necessary in the case of corresponding diverter switches, which likewise leads to an increase in the cost.